A goal of geneticists for the last fifty years has been to construct a high-resolution map of the human genome. Early studies relied entirely on meiotic mapping methods, which provided low-resolution maps of the chromosomes. The use of restriction fragment length polymorphisms has made it possible to improve this resolution and construct genetic linkage maps of all 23 human chromosomes and to localize genes responsible for inherited diseases. However, the limit of resolution of these meiotic maps is on the order of a few million base pairs (Mbp). On the other hand, the development of molecular cloning techniques has provided powerful tools to examine DNA of smaller size, in the range of thousands of base pairs. However, complete high-resolution maps of even the smallest human chromosomes have not yet been constructed because of their enormous size. Recent advances in somatic cell genetics, large DNA electrophoresis, and in situ hybridization have helped to fill the gap between these genetic and physical maps, allowing the mapping of regions of DNA in the size range of several hundred kilobasepairs (kb). They study proposed here will establish a coordinated Genome Center to mount an organized effort to construct a detailed map of human chromosome 4. A combination of these new mapping technologies, including a recently- developed somatic cell procedure called Radiation Hybrid (RH) mapping, and genetic and molecular cloning methods will be used to delineate a map in the size range of several hundred kb. The chromosome will initially be broken into ten different compartments of approximately 20 Mbp each. About 40 DNA probes in each compartment will be ordered by RH mapping, followed by large-insert cloning of these 40 regions to produce a physical map of ordered DNA clones. Polymorphic DNA markers will be generated from these ordered clones to produce a high resolution genetic linkage map. The concomitant construction of in situ, RH, physical and genetic maps will provide a powerful means to produce a comprehensive map of the chromosome efficiently.